Thursday, April 22, 2010

Making Healthy Probiotic Yogurt

Sometimes being healthy requires an arduous discipline, but making and eating fresh homemade yogurt is one of the fun parts about good health. Below are the materials I use to make yogurt.

I prefer using an electric yogurt maker, but it is possible to make yogurt without one as many cultures have for centuries. The main ingredient is fresh milk. Organic whole milk is best if you can get it, but any milk will do that does not have antibiotics in it which can kill the organisms. Even UHT milk or powdered milk can work. I prefer to add about 1/2 cup of cream (125mL) to one quart (1 liter) of milk to make it richer, but the amount of milk fat is personal preference.

Yogurt makers can have one large bowl or several individual one serving size containers. I prefer one that has a large glass bowl, but stainless steel or plastic will also work. For best results, I sterilize the bowl with boiling water. Then, I fill it with the milk and cream mixture and place it the microwave. Through trial and error and use of a food thermometer, bring the milk to about 180-200° F (92-95° C). This serves two functions, it sterilizes the milk so there are no unwanted bacteria giving it an off taste, and it slightly modifies the milk so it is smoother when it ferments and does not curdle.

Using a food thermometer, let the milk cool to 108-112° F (42-44° C). Usually, a skin will form on the surface. Many people skim this off. It is milk protein and I prefer to blend it back in with a little battery powered hand blender. At this point, you may add one packet of probiotic yogurt starter. I picture the YĆ³gourmet brand probiotic yogurt starter above which has five strains including the two normal yogurt strains and three probiotic strains. You can read about it here. There are several good probiotic yogurt starters in China but they are formulated to make a thinner drinking yogurt. I use two packets of the Chinese yogurt starters to get a thicker yogurt.

As you can see from the above chart, the length of the fermentation will affect (1) the amount of carbohydrate in the form of lactose (milk sugar), (2) the sourness of the yogurt determined by the amount of lactic acid, and (3) the amount of live micro-organisms. Commerical yogurt is only fermented for 4-5 hours. Most people ferment home yogurt for 8-10 hours. The Specific Carbohydrate Diet for people with autoimmune diseases recommends fermenting yogurt for a full 24 hours and then straining it to get the lowest possible lactose content as lactose is a potent allergen for many people. I generally ferment my yogurt for 20-24 hours to get the most probiotic organisms and the lowest carbohydrate. I like the tarter taste of a fully fermented yogurt, but some may prefer a more mild taste.

Dripping or straining yogurt will make it thicker and change the composition. Traditionally, cheese cloth is used to strain it, but I prefer to use a simple paper coffee filter or a reusable nylon coffee filter which I place in a cylindrical container to catch the liquid which drips off. The liquid portion that drips off will contain water, lactic acid and some residual lactose. Very little micro-organisms, protein or fat will drip through. A dripped yogurt will be slightly less sour, much thicker, lower carb (less lactose), higher protein and have more concentrated probiotic organisms.

If you drip the yogurt for about an hour, you will reduce the volume about 25% and get thicker Greek style yogurt. If you drip the yogurt over night in the refrigerator, you will reduce the volume over 50% and you will get thick yogurt cheese, which is almost like cream cheese in taste and usage.

Remember that yogurt is a live food and be sure to eat it fresh. Even when stored in the refrigerator, it can lose more than half of the live organisms within a week. And it tastes great fresh!


  1. Is it true that yogurt in the store has falsely high carb content because they don't know how much has been fermented?

  2. Denny, I like fully fermented, sour and thick yogurt. I don't feel the need to add anything to it to change its taste in any way. Thick, sour yogurt (or "curds" in British English) is a treat by itself.

    My question is, does fermentation really help reduce the carb content? From your graph, I see that the more the milk ferments the less the lactose (hence the less the carb content) but the more the amount of lactic acid. Once you ingest lactic acid, wouldn't the liver re-convert the lactic acid into glucose through gluconeogensis, assuming that the process of digestion does not do this already? Your graph shows that the process of fermentation does not significantly reduce the sum of lactose and lactic acid. So, does fermentation really help reduce the carb content?


  3. Keith,

    I think everybody tries to comply with FDA labeling regulations. There is some permissible tolerance, but wouldn't you want to error on the low side of carbohydrate and calories rather than the high side?

    I believe that the listed grams of carbohydrate listed on the Nutrition labels of commercial yogurt really is the best estimate. Why are the carbs so high? Commercial yogurt is general only fermented for four hours, so not that much lactose is fermented away. Commercial yogurt also includes extra lactose in the form of added milk powder.

    Another good reason to make your own.

  4. Rad,

    Any idea what bacteria are used in traditional Indian yogurt? I imagine you could make it even healthier by adding some probiotic strains.

    My understanding is that when lactose is converted to lactic acid, the body does not process it as a carbohydrate. Perhaps Professor Keith can help us better understand the chemistry.

  5. Denny,

    The "starter" that people use in India for yogurt making is the previous day's yogurt. This normally continues unbroken for years. If this "chain" is broken as when you move to a new place etc., what is generally done is to borrow a little 'starter' yogurt from persons you know - like relatives, friends, neighbours etc., who again might be running such a "chain" for years. I have heard that you can start a chain afresh by starting with pouring a little lemon juice in milk or leaving a copper or nickel coin in the milk overnight. So far, we never had to try these two alternatives. I tried to do a Google search to find which bacteria are found in Indian yogurt but am unsuccessful.

    Yes, I plan to start a new chain of yogurt with probiotics.

    Another question. If you start a chain once with probiotics, do we have to add the probiotic starter everytime we make yogurt or the probiotic yogurt of the previous day will do as a starter?


  6. The two strains that are used in nearly all yogurts are L. bulgaricus and S. thermophilus which give yogurt its characteristic taste and texture. They are very hardy in milk and can be used over and over in successive batches. Unfortunately, these two strains do not colonize the gut and are not very probioitic.

    There are many probiotic species of Lactobacillus and Bifidobacterium that can colonize the human gut creating a powerfully healthy gut ecology. Outside of the human body in the milk medium, however, they cannot compete with S. thermophillus and L. bulgaricus in successive batches of yogurt. If you try to make successive batches of probiotic yogurt using the old yogurt as a starter, the second batch will taste fine but have greatly reduced numbers of probiotic micro-organisms. In successive batches, the probiotic strains are completely crowded out.

    This is why you need to add a fresh packet of sealed freeze dried probiotic yogurt starter each time you make probiotic yogurt. You should only use probiotic starters that are individually packaged in sealed packets as they quickly degrade when exposed to any moisture in an environment where they do not have lactose to feed on.

  7. Looks delicious... How long does the process take?

  8. Marta,

    Low-carb probiotic yogurt ferments for a full 24 hours, but the actual time spent doing it is not much.

    Regular yogurt made with conventional starters takes only eight hours to ferment. Probiotic yogurt starters contain less of the normal yogurt strains and more probiotic strains. The probiotic strains are not as robust in the milk medium and take longer to get established, but they do better inside the human body.

    You can get a good tasting yogurt in just 10-12 hours with probiotic starters, but fermenting a full 24 hours will further reduce the lactose. As you know, lactose is a potent allergen for many people and can be inflammatory. It is a simple carb that can spike the blood glucose of diabetics if you consume too much.

    Have you made any yogurt? How did it go?